Changes in synaptic strength and presynaptic release at the PP synapses
Functionally, the glutamatergic inputs to the DG convey distinct types of somatosensorial information. The MPP conveys spatial information from the MEC, and the LPP transfers multisensorial information from the LEC (Hunsaker et al., 2007; Fernández-Ruiz et al., 2021). Moreover, the synaptic transfer is sustained by axons with unique electrophysiological properties that determine plasticity capabilities and the pace and strength of neurotransmitter release(Petersen et al., 2013; Collitti-Klausnitzer et al., 2021). Those synaptic features have been robustly demonstrated in this study. Consistent with previous works (Segev et al., 2020; Márquez et al., 2023), our FV and PPF analyses revealed that MK-801 alters the FV amplitude (or presynaptic action potentials) and glutamate release. Dysregulation in the propagation of the FV and the subsequent activation of the molecular machinery underlying glutamate release may explain the reduced strength of the glutamatergic transmission found in the MPP synapse. In line with this possibility, transient hypofunction of NMDARs interferes with the functional expression of presynaptic proteins that control neurotransmitter release in animal models of schizophrenia (Maher and LoTurco, 2012; Saggu et al., 2013) and schizophrenic individuals (Egbujo et al., 2016). Finally, the altered neurotransmitter release process in the MPP compared to the LPP synapse of MK-801-treated animals may suggest a marked dysregulation in transferring spatial information but not non-spatial information from the PP to the DG, a phenomenon that requires additional investigation.